In the art of laboratory experimentation with mice and rats, monitoring of body temperature is carried out by means of rectal thermistor probes. Repeated insertion of such probes will elevate temperature and therefore use of chronically indwelling probes is preferable. In this situation, the animals must be restrained less they injure themselves or destroy the equipment. To accomplish this, it is now customary to employ commonly available restraint apparatus of various types, all of which are understood to be of a construction designed to constitute an enclosure body such as a box, cylinder or the like in which an animal may be confined. It has been found, however, that confining an animal in this way in an enclosure body is undesirable as it seriously interferes with normal thermoregulatory behavior.